1. Field of the Invention
The subject invention relates to a vehicle testing assembly having an improved construction.
2. Description of the Prior Art
Vehicle testing assemblies are widely used throughout the automotive industry for research, development, performance testing and for simulating driving conditions for vehicles. The vehicle testing assemblies can include roll test machines, which are typically used in a manufacturers plant at an end of an assembly line, and dynamometers, which are commonly used in a laboratory environment. The roll test machines are used to verify that all vehicle systems are operating correctly once the vehicle is built. The dynamometers provide precise measurement and controls which can duplicate real world conditions. Both the roll test machines and dynamometers provide a test bed for the vehicle that allows the vehicle to accelerate, run at a certain speed, and decelerate, while remaining in one place. The roll test machines can simulate real world conditions but does not duplicate them as precisely as a dynamometer.
Typically, the testing assembly of either the roll test machines or the dynamometers includes a large platform for supporting the weight of the vehicle. A single large roller and/or a pair of cradle rollers are disposed below the platform to rotate the vehicle wheels, and measure and record a desired characteristic of the vehicle. In particular, the larger roller and/or pair of cradle rollers engage the wheels of the vehicle such that the roller(s) are rotatably connected to the vehicle power train to simulate driving conditions. The roller(s) is designed with internal resistors and other features to accurately simulate real world driving conditions. In other words, the vehicle drives on the roller or pair of rollers in the same manner as on the road. Examples of vehicle testing assemblies incorporating single and cradle rollers are shown in U.S. Pat. Nos. 3,490,276 and 5,311,770.
During the use of a vehicle testing assembly for a two wheel drive vehicle, the non-driven wheels of the vehicle are held stationary on the testing assembly while the driving wheels of the vehicle rest upon the roller or rollers. The roller or rollers can be rotated by the power train of the vehicle through the wheels or can be rotated by a separate drive unit, which in turn rotates the wheels of the vehicle. During the use of a vehicle testing assembly for a four wheel drive vehicle, the vehicle is held stationary on the testing assembly while both front and rear rollers engage the driving wheels of the vehicle. The vehicle may be held stationary by securing the frame of the vehicle or by the roller configuration, i.e., using cradle rollers or retaining rollers. In either of the scenarios outlined above, numerous characteristics of the vehicle may be tested.
Often, the contact surface of the roller is simply smooth turned steel. Although cost effective, the smooth steel surface promotes tire damage under certain testing conditions. In particular, when the tire becomes excessively heated, the tires ability to resist tearing is weakened. The excessive heating occurs from the flexing or deformation of the rubber tire at the surface of the roller, rapidly compressing air at the point of contact between the tire and roller, and frictional heat created when the tire and roller slip. A tire slipping on the roller will grab and release from the roller which frequently causes tearing of the overheated tire. The slipping and damage frequently occurs during vehicle braking tests. In particular, if the driver testing the vehicle applies excessive pedal force, the tires may stop too quickly on the rollers, thereby causing the tires to slip on the roller. As the excessively heated tire tears, blocks of rubber, known as chunks, break off from the tire tread face of the tire. Rubber residue from the chunks and tire compound from the tire production process become attached to the steel roller to create xe2x80x9cdustxe2x80x9d buildup which causes a non-uniform contact surface on the roller. In addition, when chunking damage occurs, it is costly for vehicle manufacturers as the tire must be replaced.
In order to reduce the temperature of the tire roller interface, and thereby reduce subsequent tire damage, it is desirable to cool the surface of the roller. An example of a roller which includes some type of cooling mechanism is disclosed in U.S. Pat. No. 3,982,428. The ""428 patent discloses a roller which has a pair of helical grooves formed therein. These grooves, however, do not, by themselves, provide the requisite cooling in order to prevent all tire damage.
Accordingly, it would be desirable to incorporate additional and/or alternative methods for cooling the roller or rollers of the roll test machine and dynamometer. Additionally, it would also be desirable to develop a roller which has reduced acoustical noise and does not accumulate tire rubber on the contact surface of the roller.
A vehicle testing assembly for performing tests to determine certain characteristics of a motorized vehicle having at least one wheel. The testing assembly comprises a roller having an annular configuration with an outer surface. The roller is formed of a roller composition. A controller is connected to the roller for retrieving data from the roller during a rotation of the roller. The testing assembly is characterized by a coating applied to the outer surface of the roller to define a contact surface of the roller. The coating is formed of a coating composition different from the roller composition. During operation of the vehicle testing assembly, the wheel of the vehicle continuously contacts the contact surface of the coating to provide an accurate testing of the characteristics of the vehicle as the roller rotates.
The subject invention therefore includes an improved roller which reduces the heating of the tire, the noise generated from the tire and roller contact, and the accumulation of tire rubber or xe2x80x9cdustxe2x80x9d buildup on the roller surface. The coating is of a unique composition which is discussed in greater detail below. In addition, grooves may also be incorporated into the roller to provide additional cooling and noise reduction.